In the present invention, distribution of adjoining pixels is reflected in density distribution of objective recording pixels so that high quality recording can be conducted. The present invention relates to a color image forming apparatus in which: one matrix pixel image data is divided into small pixels m.times.n (the width.times.the length) considering the adjoining pixel data, and after that, the center of gravity of each line is found; the phase of the reference wave is deviated according to the center of gravity; and dot recording composed of n small scanning lines is conducted by the modulated signal of the pixel density data modulated by the reference wave signal so that a character and a halftone image can be reproduced. The recording apparatus of the present invention is used for a printing apparatus or a displaying apparatus.
In the field of image forming apparatus using the electrophotographic method, a digital halftone image is reproduced in the following manner: an original image is read by a scanner to get on image signal; and image density data in which the image signal is gradation-corrected, A/D converted, and shading-corrected, is modulated by a reference signal and thus a digital image is obtained.
When an original image is read by the scanner, an edge portion of the image is read in a halftone density due to the aperture of a solid state image pick-up element installed in the scanner. When a latent image is formed on a photoreceptor with an image density data obtained from image signals, recording pixels corresponding to the edge portion of the latent image are recorded in recording pixels on an average basis. Therefore, the sharpness of the recorded image is lowered. For this phenomenon, in the past, there has been known a method to apply an MTF correction by means of image-sharpening by the use of a differential filter, or a Laplacian filter on image signals. In this method, however, edge portions only are enhanced, and uniformity of halftone images is relatively lowered.
On the other hand, even when an interpolated character or figure is formed from computer graphic (C.G.) data or font data, a similar problem is caused. That is, when the edge portion is interpolated smoothly with the intermediate density using the interpolated data, a recording pixel corresponding to the edge portion is recorded in pixels as average density, and thereby the resolution is lowered in the same way as the aforementioned.
For the reasons mentioned above, intermediate density processing, which effectively operates on the edge portion of the image, is required.
Further, when intermediate density processing is conducted on each color in a color image forming apparatus, there occurs the problem in which color tone is varied, or characters become not sharp.
Further, the invention relates to an image forming apparatus wherein dot-recording is made for reproduction of characters and halftone images by a laser diode oscillated by modulation signals in which density data are modulated by reference signals.